The long-term goal of our research program is to understand the neural circuit mechanisms underlying motivated behavior. The exquisite neural architecture of microcircuits in prefrontal cortex (PFC) is thought to underlie the flexibility and dynamics responsible for cognition. This proposal aims to understand the role of distinct interneuron types in prefrontal cortical function. Our general approach is predicated on the idea that access to cell-type identity is essential to unlocking the function of neocortical circuits. Because interneurons constitute a highly diverse neural population, some with well-understood anatomical specializations, they represent both an important opportunity to reveal microcircuit function as well as an excellent showcase for demonstrating the use of cell-type identity based functional studies. Our first objective therefore is to develop an optogenetic toolkit for this purpose. We will design and validate a miniature microdrive for combined electrophysiological recordings and fiberoptic stimulation that is light-weight and suitable for chronic recordings from freely behaving mice - enabling us to identify, record and manipulate genetically labeled cell-types. We propose to study three non-overlapping classes of interneurons: the parvalbumin (PV), somatostain (SOM), and vasoactive intestinal peptide (VIP) positive cells using knock-in Cre-driver lines, each with distinct functions. Using these tools we will examine how distinct cortical brain rhythms, signatures of coordinated neural activity, are correlated with the firing of distinct interneuron subtypes. Our optogenetic approach will not only establish the correlation of interneuron subtypes with oscillations but also enable selective control over the activity of distinct interneuron subtypes to pursue the mechanisms for generating different brain rhythms. We will employ a loss-and-gain-of-function approach to abolish and induce different brain rhythms in behaving animals. If successful, the proposed research is expected to result in a detailed understanding of the role of distinct interneuron subtypes in prefrontal cortical function and behavior. Because maladaptive changes inhibitory interneurons have been linked with a diverse set of diseases from epilepsy to schizophrenia and autism, our results will have direct implications for interpreting deficits in these disease states and potentially suggest avenues for remediation.